Phosphorylation events regulate cell function in a multiplicity of pathways. Despite the effort to understand the molecular mechanisms that govern sperm function, there is still very little known. Recently, a family of testis specific serine/threonine kinases was described. However, the characterization of this family, their activation and substrates as well as their specific function remains to be discovered. We have found evidence of these kinases in mature sperm both in mice and in humans. We have also found an interesting conservation pattern that dates back to invertebrates keeping the testis specificity. Because of these findings we believe that this family of kinases plays an important role in spermatogenesis and/or sperm function. In this proposal we propose to further describe and attempt to characterize this family of kinases focusing our effort in the mammalian members and utilizing the mouse model with a variety of biochemical, molecular biology and cell biology techniques.